Power shovel



K. SCHNEKDER POWER- SHOVEL Apr-H 29, 3958 I 4 Sheets-Sheet 1 Filed May12, 1954 INVENTOR ATTORNEY Aprifi 9, 195% IN. SCHNEIDER POWER SHOVEL 4Sheets-Sheet 2 Filed May 12, 1954 I INVENTOR MM ATTORNEY 1958 1K.SCHNEIDER 2,832,485

POWER SHOVEL Filed May 12, 1954 4 Sheets-Sheet 3 INVENTOR mam Qm//M ATTOR NEY K. SCHNEIDER POWER SHOVEL vApril 29, 1958 4 Sheets-Sheet 4 FiledMay 12, 1954.

INVENTOR ATTORNEY Unite States Patent POWER SHOVEL Karl Schneider,Greenfield, Wis., assignor to Harnischfeger Corporation, Milwaukee,Wis., a corporation of Wisconsin Application May 12, 1954, Serial No.429,235

8 Claims. (Cl. 214-136) This invention relates to excavating machineryand it more specifically resides in a power shovel having a forwardlyinclined boom and a tiltable elongate mast rising above the boom thatpivotally connects at the upper end with a forwardly extending dipperstick that has crowding and retracting motions imparted thereto byaltering the degree of tilt of the mast, the mast being controlled by acrowd line extending forwardly from the mast to the boom and a retractline extending rearwardly from the mast, and the shovel furtherincluding hoist means for a dipper carried by the dipper stick thatincludes a line attached to the dipper that may be drawn upwardly toimpart a digging motion to the dipper.

In a conventional power shovel the dipper stick is mounted directly uponthe boom in a position substantially medial of the boom ends. In thisposition the dipper stick is pivoted about its mounting in response tomovements of the hoist cable, and it is attached in a manner to permitlongitudinal movement transversely of the boom to effectuate the crowdand retract motions. With the dipper lowered and moved rearwardly tocommence a digging motion at the immediate front of the shovel the hoistline will run downwardly along and in close proximity to the undersideof the boom. The line thus passes within a small distance of the dipperstick pivot and the moment arm is small. Upon drawing in the hoist linethe digging capacity for this dipper position will accordingly begreatly diminished from that otherwise obtainable when the dipper is ina relatively forward position and the hoist line is at a substantialdistance to the front of the dipper stick pivot.

. In the present invention the dipper stick is free of the boom and is,instead, attached at its rearward end to a tiltable mast. This mast iselevated toward the vertical when it is desired to lower dipper andshift it rearwardly to commence a digging stroke. With the mast elevatedthe pivot of the dipper stick is well to the rear .of the boom and theangular incidence of the hoist cable to the dipper stick is greater thanfor the conventional shovel. The effective digging capacity is thusenhanced for a dipper position to the immediate fore of the shovel cab.This form of apparatus is of particular advantage Patented Apr. 29, 1958angle to both the dipper stick and the mast. As this crowd line is drawnin the pivoted connection of the mast and dipper stick is drawnforwardly, and with a lifting force being applied through the hoistcable to retain the dipper in raised position the crowd line urges themast and dipper stick toward a longitudinal alignment. With suificientangular displacement between the crowd line and the mast and 'dipperstick being provided in the geometry of the structure the appliedcrowding force along the dipper stick will become materially greaterthan that applied through the crowd line. There is thus achieved thedesired crowding force without need of employing undesirably large andbulky control apparatus in the cab of the shovel.

it is an object of this invention to provide a power shovel withimproved digging characteristics wherein the dipper may be lowered tothe immediate front of the cab and a digging force exerted through thehoist cable that provides enhanced digging capacity at this position.

it is another object of this invention to provide a power shovel whereinthe crowding action is enhanced upon thrusting the dipper into aforwardly extended position.

It is another object of this invention to provide a power shovel havingthe dipper stick and dipper mounted on a mast independent of the boom,whereby a boom of lighter construction may be employed.

It is another object of this invention to provide a power shovel whereinthe load of the dipper stick and dip-per is partially sustained by asupplementary mast to reduce the strain otherwise imposed upon the boomby the digging and swinging movements of the dipper.

It is another object of this invention to control the motion of a dipperstick through a pair of crowd and retract lines wound uponsimultaneously driven drums that retain the lines taut at all times forimmediate re sponse to either a crowd or retract action of the controlcables.

These and other objects and advantages of this invention will appear inthe description to follow. In the description reference is made to theaccompanying drawings, which form a part hereof, and in which there isshown by way of illustration and not of limitation a specific form inwhich this invention may be embodied.

In the drawings:

Fig. 1 is a side view in elevation of a power shovel in i which thisinvention is embodied,

for stripper shovels, wherein extended digging motions are made along ahorizontal terrain to shovel.

The invention also presents an apparatus that provides crowding forcesat the dipper of large magnitude, that may exceed the operating forcesapplied to the dipper stick, upon moving the dipper into a positionrequiring the application of the larger magnitudes of crowding force. Asa dipper is moved through its digging stroke and is thrust b'othoutwardly and upwardly into an ex-. tended raised position, *beyond theend of the boom, the required crowding force reaches maximum values. To

the front of the apply an ample crowding force to a dipperin an extendedraised position there is employed a crowding line running from the mastto the boom at a substantial Fig. 2 is a fragmentary top plan view ofthe power shovel showing the boom, mast and portions of the dipperstick, with the mast and dipper stick extended longitudinally along theboom,

Fig. 3 is a fragmentary side view in elevation of the lower ends of theboomand mast showing the pivotal connection therebetween,

Fig. 4 is a clear view in elevation and partly in section of cable drumsfor the control of crowd and retract cables that are joined to the mast,viewed through the plane 4-4, and

Fig. 5 isa side view in elevation and in section of the cable drums forthe crowd and retract cables viewed through the plane 5-5 shown in Fig.4.

Referring now to the drawings,- for the purpose of describing a specificembodiment of the present invention. there is shown in Fig. 1 a strippershovel 1 having a cab 2 mounted upon a crawler frame 3. A gantry 4 isprovided for the shovel 1 that comprises a pair of vertical tensionmembers 5, one of which is seen in the side view of Fig. 1, that aresecured at the lower ends to the cab' platform within the interior ofthe cab .2, and which extend upwardly above the roof of the cab 2 toconnections with plates 6. A pair of compression 6 and extend forwardlyu and downwardly to connections with the platform of the cab 2, whichconnections are not shown. An operators station 8 is provided at theright forefront of the cab 2, and mounted at the forward end of the cab2 is an upwardly extending tilted boom 9. A set of staylines extendbetween the upper end of the boom 9 and the gantry 4 to retain the boom9 in a fixed position. Also carried by the cab 2 is a hoist cable drum11 and a crowd and retract cable drum assembly 12, which will behereinafter more fully described when reference is made to Figs. 4 and5. The drum 11 and drum assembly 12 are driven and controlled bymachinery not shown.

As is clearly shown in Figs. 2 and 3, there is pivotally mounted to theupper side of the base of the boom 9 a tiltable mast 13. The mast 13includes a pair of parallel legs 14 spaced from one another at adistance slightly greater than the breadth of the main run of the boom9. The lower end of each mast leg 14 is hinged to a set of plates '15attached to the top side of the boom 9, and a reinforcing member 16 isextended between the lower ends of the mast legs 14. A bracket 17 isattached to the upper side of the reinforcing member 16 and supports arotatable cable sheave 13, the pivot of which is displaced as the mast13 is tilted with respect to the boom 9, as is shown in Figs. 1 and 3.

A fabricated reinforcing 19 extends between and spaces the upper ends ofthe mast legs 14. The reinforcing 19 presents a pair of brackets 29 onthe topside of the mast 13 for connection to a pair of retract lines 21and a pair of brackets 22 on the underside of the mast 13 for connectionto a pair of crowd lines 23. The underside of the reinforcing 19presents an abutment 24 to a set of shock absorbers 25 mounted uponseveral bracket plates 26 on the topside of the boom 9 in a position tolimit the forward tilt of the mast 13. Also mounted by the bracketplates 26 are a pair of rotatable sheaves 27 about which are passedthecrowd lines 23.

After passing about the sheaves 27 the crowd lines 23 pass downwardlyalong the upper side of the boom 9 toward the cab 2. The lines 23terminate in connections with a cross tie 28 that is in turn joined to asingle crowd cable 29 that passes beneath the cable sheave 18 and henceto the drum assembly 12. The pair of retract lines 21 extend rearwardlyfrom the upper end of the mast 13 and pass about two of a set of sheaves30 mounted upon the gantry 4. The lines 21 are then connected through across tie 31 to a single retract cable 32 which leads downwardly to thedrum assembly 12. Upon operation of the drum assembly 12 the crowd cable29 and retract cable 32 will be simultaneously operated, whereby onewill be drawn in while the other paid out so as to shift the mast 13from one position of tilt to another.

Pivotally joined to the upper end of the mast 13 is a 7 two armed dipperstick 33 that extends forwardly and passes to the front of the boom 9.Each arm of the dipper stick 33 is closely spaced to one of a pair ofbearing bars 86 on the sides of the boom 9, against which the stick 33may bear either during a digging operation or a swinging of the cab 2. Adipper 34 is mounted on the forward end of the dipper stick 33, and adipper sheave 35 is pivotally mounted through a bail 36 to the top ofthe dipper 34. To control raising and lowering of the dipper 34 a hoistcable 37 is led upwardly from the hoist drum 11 around one of the set ofsheaves 30 on the gantry 4 and hence forwardly to the top of the boom 9,where it passes about one of a pair of boom sheaves 38 and then runs tothe dipper sheave 35. The hoist line 37 passes about the dipper sheave35 and returns to the boom sheaves 38 and then extends rearwardly to adead end connection with the gantry 4.

Referring now specifically to Figs. 4 and 5, there is shown the retractand crowd cable drum assembly 12. A drive shaft 39 is-borne'at its endsby bearings 40 mounted within support housings 41. Keyed to the righthand end of the shaft 39 is a gear wheel 42 of large diameter that is inmesh with a driving gear, not shown. Rotation of the gear wheel 42 willcause similar rotation of the drive shaft 39, and keyed to the shaft 39at the side of the gear wheel 42 to rotate therewith is a sun gear 43forming apart of a planetary system to be described. The planetarysystem includes a support 44 for a set of planet gears 45 that isrotatably mounted by a bearing 46 seated upon the hub of the gear wheel42 and a bearing 47 seated upon the sun gear 43. The planet gears 45 arein mesh with an internal orbit gear 48 that is bolted to a crowd cabledrum 49.

A plurality of spokes 59, each braced by a web 51, extend radiallyoutwardly from the planet gear support 44 to support a brake drum 52that is encircled by a brake lining 53. Disposed in facing relation tothe lining 53 is a brake band 54 that is shown in brake releasedposition, and which may be brought into braking engagement with thelining 53 by operation of means not shown. Upon engaging the brakemembers 53, 54 the planet gear support 44 is held in stationaryposition, and each planet 45 will be rotated by the sun gear 43 to drivetheorbit gear 48 in a direction of rotation opposite that of thedrive'shaft 39. The crowd cable drum 49 is moved in a likedirection. Thedrum a9 is rotatably supported at one end upon the drive shaft 39 by abearing set 55, and extends axially to the left, as viewed in Fig. 4, toterminate in a hub 56 that encircles and is borne by a hub 57 of aretract cable drum 58. A sleeve bearing 59 separates the hubs 56 and 57to permit a limited angular displace ment to occur between the drums 49and 58. To rotatably mount the retract cable drum 58 a roller bearingset 69 supports the hub 57 upon the drive shaft 39, and a set of taperedbearings 61 are interposed between the shaft 39 and the left side of thedrum 58.

Bolted to the left side of the retract cable drum 58 is a double brakeand clutch rim 62 that presents an outer brake member 63 with a brakelining 64 and an inner clutch member 65. A brake band 66 surrounds andisin facing relation to the brake lining 64 for a braking engagementtherewith. It is the purpose of the brake members 64, 66 to restrainrotation of the cable drums 49, 58, upon setting the band 66 inengagement with the liningfid, to hold the mast 13 in desired position.Within the clutch member 65 is an outwardly movable clutch band 67carried by a clutch member 63 that is keyed to the drive shaft 39 forrotation therewith. Means, not shown, are provided for moving the clutchband 67 into engagement with the clutch member 65, whereby the retractcable drum 53 may be driven by the shaft 39 in a like direction ofrotation.

Formed as an integral part of the hub 56 of the crowd cable drum 49 aretwo pair of radially extending brackets 69 that are diametricallyopposed from one another, as shown in Fig. 5. Each pair of brackets isnotched, as at 70, to receive trunnions 71 from the sides of the heads72of eac-h of pair of cylinders 73. Each cylinder 73 is free to ro'ckwithin the associated notches 7'1) and an inlet connection 74 at theafter end is made with a flexible hose 75 through which a fluid underpressure may be introduc'ed to the interior of the respective cylinder73 to work against a piston, that is not shown.

To provide a fluid pressure source an accumulator vessel 76 is mountedwithin the crowd cable drum'49, as is shown in Fig. 4, and a fluid line77 that connects with the outlet of the accumulator vessel 76 extendstouch of the hoses 75. Extending from the head 72 of each cylinder 73is-a piston ram 78 each of which will be urged outwardly fromits-respective cylinder 73 upon the introduction of a fluidunderpressure to within the cylinder 73. The end ofeach piston ram 78 carriesa fitting 79 that'is disposed within asocket 80 attached to the retractcable drum'58 by a pair of brackets 81 and 82. A pin "83 passes throughside walls of each'socket 80 and throu'gh the associated fitting 79 toretain the fitting 79 within the socket 80 and fixed with respect to theretract cable drum 58. a

Upon the piston rams 78 being moved outwardly from the cylinders 73 thesockets 80 will be displaced away from the brackets 69 and a rotationaldisplacement between the cable drums 49 and 58 will occur. This angulardisplacement will be restricted by the crowd cable 29 and retract cable32 which are wound about the drums 49 and 58in a fashion to lead fromthe drums 49, 58 in opposite directions. As the drums 49, 58 areangularly displaced by action of the cylinders 73 the cables 29, 32 are,each wound upon the respective drums 49, 58 and placed in tension. Witha suflicient tension in the cables 29, 32 the pressure in the cylinders73 will be balanced. The radially inner faces of the sockets 80 areformed to present lobes 84 that will engage with and abut against a pairof radially extending stops 85 on the hub 56 of the crowd cable drum 49.The lobes 84 and stops 85 limit the angular displacement of the drums49, 58 that may occur in response to the tensioned crowd and retractcables 29, 32. In Fig. the lobes 84 and stops 83 are shown in abuttingposition, as may be assumed upon rigging the cables 29, 32 and lines 21,23 and before fluid pressure is introduced in the hydraulic cylinders73. In the usual course of operation the lobes 84 and stops 85 will beseparated by angular displacement sufficient to permit relative movementbetween the cable drums 49, 58in either direction.

The crowd cable and lines 23, 29 and the retract cable and lines 21, 32are connected between the drum assembly 12 and the upper end of the mast13 to form a closed circuit. This circuit has a geometrical perimeterdefined by the crowd cable leading from the drum assembly 12 forwardlyto and about the cable sheave 18 at the base of the mast 13 and hencealong the upper face of the boom 9 where connection is made with thecrowd lines 23, that pass about the sheaves 27 to a connection with thebrackets 22 at the upper end of the mast 13. The circuit is continuedfrom the brackets 20, also at the upper end of the mast 13, by theretract lines 21 that ex tend rearwardly and pass about a pair of thegroup of sheaves 30 to connect with the retract cable 32 that is in turnwound upon the drum assembly 12.

Toperform a digging stroke for the shovel 1 the clutch band 67 isengaged with the clutch member 65 to rotate the drum 58 for drawing inthe retract cable 32. The mast 13 will rise and the crowd cable 29 willnecessarily be drawn from the drum 49, which therefor rotates with thedrum 58. The connections between the drums 49, 58 formed by thecylinders 73 and piston rams 78, urge the drums, as has been noted, tomove relative to one another to retain both the retract and crowd cablestaut. In this fashion the mast 13 may be raised to the position shown inphantom in Fig. 1, and the hoist cable 37 is simultaneously payed out toallow the dipper 34 to swing downwardly to the fore of the crawler frame3,. as is also shown in phantom in Fig. 1.

Digging is now commenced by drawing in the hoist cable 37 to pivot thedipper stick 33 and dipper 34 about the connection with themast 13. Thispivotal connection is disposedat .a substantial distance from the run ofhoist cable 37 extending from the boom sheave 38 downwardly andrearwardly along the underside of the boom 9 to the dipper sheave 35.The moment arm for the digging force applied through the hoist cable 37is consequently substantial and the digging action is materiallyenhanced over that of a shovel mounting the dipper stick directly uponthe boom wherein the moment arm for the digging force will be quitesmall.

The operator coordinates the digging motion with a crowding motioneffected by releasing the clutch band 67, that had been employed forretracting the mast 13,

as shown in Fig. l.

A raising, or lowering, of the mast 13 causes a change in theperimetrical length of the circuit defined by the crowd cable and lines29, 23 and the retract cable and lines 32, 37. To accommodate for thisvariation the cable sheave 18 mounted at the lower end of the mast 13will swing with a shift in tilt of the mast. 13, as is shown in Figs. 1and 3. With a rise of the mast 13, the sheave 18 will move to a lowerposition, and consequently the required run of cable and line betweenthe crowd cable drum 49 and the sheaves 27 on the boom 9 is increased.The increase compensates for a decrease that would otherwise occur inthe amount of cable and line required to complete the circuit.Conversely, as the mast 13 is lowered the cable sheave 18 rises toeffectively decrease the circuit length and compensate for increasedlength of cable and line otherwiserequired for the circuit.

It is not intended that the movements of the cable sheave 18 at the baseof the mast 13 compensate precisely for the variations in circuit lengthcaused by a shift of the mast 13. Such actual change in circuit lengththat may occur will be accommodated, however, through the.

action of the cylinders 73, which permit limited angular displacement tooccur between the drums 49 and 58. If the circuit perimeter decreasesthe piston rams 78 move outwardly from cylinders 73 to draw in either,or both,

the cables 29, 32 and retain each under tension. On the other hand, anincrease in circuit perimeter will cause more cable to be payed out thanis wound in and the piston rams 78 will be retracted within thecylinders 73.

The crowding motion of the shovel of this invention is enhanced througha desirable employment of a mechanical advantage. As the dipper stick israised and crowded forwardly the run of crowd line between the mast endbrackets 22 and the sheaves 27 will assume a position at a substantialangle with both the mast 13 and dipper stick 33. The lower end of themast 13 being fixed, and the forward end of the dipper stick beingsupported by the hoist cable 37, the downward pull of the retract lines23 urges the mast 13 and dipper stick 33 toward a position of alignmentwith a toggle like action. The crowding force transmitted through thedipper stick 33 to the dipper 34 is of considerably greater magnitudethan that applied through the crowd lines 23. Thus, to retain a loadeddipper in a raised and forwardly extended position the crowd cable andlines are called upon to apply a force to the dipper stick 33 that isconsiderably less than the crowding force applied to the dipper.

I claim:

1. In a power shovel the combination comprising a forwardly inclinedboom, an upwardly extending elongate mast pivotally mounted at its lowerend to permit forward and rearward movement of the upper end, a dipperstick pivotally secured to the upper end of and extending forwardly fromsaid mast including a dipper at its forward end, drum means adapted todraw in and pay out line, a sheave on said boom forward of said mast, acrowd line connected at one end to said mast and extending to theforward side of the mast toward and about said sheave on said boom andhence to said drum means to be drawn in thereby for tilting the mastforwardly independently of said boom and be payed out thereby to permitrearward elevation of the mast, a retract line connected at one end tosaid mast and extending to the rearward side of the mast and hence tosaid drum means to be drawn in thereby for moving the mast rearwardlyindependently of said boom and be payed out thereby :to permit forwardmotion of the mast, and a hoist cable attached to said dipper extendingupwardly to :said boom .for drawing the dipper upwardly to pivot thedipper stick about its connection with'said mast in a digging motion.

2. In a power shovel the combination comprising a forwardly inclinedboom, an elongate mast 'pivotally mounted at its lower end and risingupwardly above said boom in a substantially common vertical planewhereby pivot may be made to cause forward and'rearward movement of theupperend of themastga dipper stick pivotally secured to the upper .endof .saidLmast and extending forwardly of said boom, a dipper .mounted on'the forward end of said dipper stick to the front of said boom, asheave on said boom, .drum means adapted to draw in and pay outline, 'acrowd line connected at one end .to said mast and extending to .theforward side of the mast toward and about said isheave .on said boom and:hence to said drum :means to be drawn in thereby for tilting the mastforwardly independently of said boom and to .be payed outthereby topermit .rearward.elevation .ofrthe mast, a retract line connected at oneendzto said mast and extending to the rearward side of 'theamast andhence to said drum means to .be drawn in thereby for moving the mastrearwardly independently of said boom and to be payed out thereby "topermit 'forwardxmotion of the mast, and a hoist .cable attached to said:dipper extending upwardly to said boom .for .drawing the dipperupwardly to pivot "the dipper stick about its connection with said mastin adigging motion.

.3. In a power shovel the combination comprising a platform, a forwardlyinclined boom rising from said platform, a sheave mounted by said boom,an elongate mast pivotally'mounted at its lower end to permit forwardand rearward movement of the upper end, .a dipper stick pivotallyconnected to the upperend of "said'mast extending forwardly therefromand terminating in a forward end mounting a dipper, a crowd line drumcarried by said platform, a retract line drum carried by said platform,a crowd line connected at one end to'said mast and led to the front ofthe :mast toward and about said boom sheave and .hence toward said crowdline drum to be wrapped thereon, a retract line connected at one end ofsaid mast running .rearwardly therefrom .eand hence toward .said retractline drum ;to..be wrapped thereon, a coupling between said crowd andretract line drums applying a bias force toithedrums urging a relativerotation between said drums whereby said ..crowd .and. retract lineswould .both be wound upon the drums, and driving means for saidcrowd andretractline drums to selectively drive either of said drums to draw intheassociated line whereby theother of said linesis payedout from itsrespective drum and said'mastis pivoted to produce movement of the upperend thereof.

4. In a power shovel .the combination comprising a platform, a forwardlyextending inclined boom secured to and rising from said platform, a mastpivotally mounted at its lower end and rising above said boom, a dipperstickincluding a dipper pivotally attached to the upper endof said mastextending acrosssaid boom with said dipper to the front of the boom, acrowd line drum mounted upon said platform, -a retract line drum mountedupon said platform, said drums .being coaxially arranged forrotation ina like direction, a sheave attached 6 tothe lower end of said mastdisplaced imposition with a motion of said mast about its pivot, a crowdline connectedat one end to'said mast running toward said boom and hencealong said boom and aboutsaid sheave to an attachment with said crowdline .drum, a :retract line connected at one end to said mast runningrearwardly from said mast and hence to an attachment with said retractline drum whereby a rotation of said drums in like direction will drawin one and pay out the other of said lines, a coupling disposed betweensaid crowd line and retract line drums including bias means urging alimited angular displacement between said drums that draws insaid crowdand retract lines to retain the same taut and driving means for saiddrum for selectively rotating either of the drums to draw in theassociated line and pay out the other line to pivot said mast and impartmovement to said dipper stick and dipper, whereby said sheave isdisplaced to maintain the combined length of crowd and retract linesextending between said drums and connections with said mast nearlyconstant and said coupling permits of angular displacement between saiddrums to compensate for variation in the combined length of crowd andretract lines between said drums and mast and to-retain the lines taut.

5. in a power shovel, the combination comprising a forwardly inclinedboom, an upwardly extending elongate mast pivotally mounted at its lowerend .to permit forward and rearward movement of the upper :end, a dipperstick pivotally secured to the upper end of and extending -forwardlyfrom said mast including a dipper at .its forward end, a sheave on saidboom forward of said mast, a crowd line connected at one end to saidmast and extending to the forward side of the mast toward and about saidsheave on said boom, a retract line connected at one end to said mastand extending to therearward side of the mast, crowd and retract lineactuating means to selectively draw in on saidlines for tilting the mastforwardly and rearwardly independently of said boom, and means formaintaining both ,crowd and retract lines taut notwithstanding changesin line geometry resultant from changes in the position of the mast.

6. The device of claimv5 -in which the means last mentioned comprises aline sheave about which said crowd line is reeved and means mountingsaid sheave .on ,the mast whereby the sheave partakes of mast movementand comprising a movement arm on which said sheave swings to take up andsupply line slack when the mastis pivotaliy moved.

7. The device of claim 5 in which the crowd and retract line actuatingmeans comprises drums, the .means last mentioned comprising means fordisplacing said drums about their axes of rotation to substantiallymaintain a predetermined tension insaid lines.

8. In a power shovel the combination comprising an inclined boom, anupwardly extending elongate mast pivotally mounted at its lower end topermit forward and rearward movement of its upper end, a dipper stickpivotally connected to the upper vend of and extending forwardly fromsaid mast, a dipper thereon and ahoist cable attached to said dipper andextending upwardly to said boom, a crowd line sheave mounted on the boomforward of said mast, a crowd line connected to said mast and reevedabout said sheave and means for tensioning said crowd line whereby to'tend to draw the 'boomand mast toward each other.

References Cited in the file'of this patent UNITED STATES PATENTS

